To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
With respect to high-energy radiation of very short wavelength such as EB or X-ray, hydrocarbons used in resist materials have little absorption. Then resist materials based on polyhydroxystyrene composed mainly of hydrocarbon are under consideration.
The exposure system for mask manufacturing made a transition from the laser beam exposure system to the EB exposure system to increase the accuracy of line width. Since a further size reduction became possible by increasing the accelerating voltage of the electron gun in the EB exposure system, the accelerating voltage increased from 10 kV to 30 kV and reached 50 kV in the current mainstream system, with a voltage of 100 kV being under investigation.
As the feature size reduces, image blurs due to acid diffusion become a problem. To insure resolution for fine patterns with a size of 45 nm et seq., not only an improvement in dissolution contrast is important as previously reported, but control of acid diffusion is also important as reported in Non-Patent Document 1. Since chemically amplified resist compositions are designed such that sensitivity and contrast are enhanced by acid diffusion, an attempt to minimize acid diffusion by reducing the temperature and/or time of post-exposure bake (PEB) fails, resulting in drastic reductions of sensitivity and contrast.
The addition of an acid generator capable of generating a bulky acid is an effective means for suppressing acid diffusion. It was then proposed to incorporate in a polymer recurring units derived from an onium salt having a polymerizable unsaturated bond as acid generator. Patent Document 1 discloses a sulfonium salt having a polymerizable unsaturated bond, capable of generating a specific sulfonic acid and a similar iodonium salt. Patent Document 2 discloses a sulfonium salt having a sulfonic acid anion directly attached to the backbone.
Attention is paid again to non-chemically-amplified resist compositions because they are not affected by acid diffusion. In the early era, it was proposed to form a positive pattern by coating a resist film containing a polymer of backbone cleavage type as typified by polymethyl methacrylate (PMMA) and developing it in an organic solvent. The resist film is increased in sensitivity by copolymerizing α-chloroacrylate with α-methylstyrene to boost the efficiency of backbone cleavage.
Patent Document 3 discloses a non-chemically-amplified resist composition comprising a polymer containing anion-bound PAG units and amino-containing recurring units, but not acid labile group-containing recurring units as a base resin. From this resist composition, a negative pattern is formed via organic solvent development.
Patent Document 4 discloses a polymer containing anion-bound PAG units and amino-containing recurring units. Since this polymer contains acid labile group-containing recurring units as well, Patent Document 4 basically relates to a chemically amplified positive resist composition wherein the acid generated from the anion-bound PAG unit is quenched with the amino group. Since both the acid generated from the anion-bound PAG unit and the amino group for quenching the acid are bonded to the polymer backbone, diffusion is minimal. However, a lowering of resolution by acid diffusion is inevitable because the resist is basically of chemically amplified type.
Citation ListPatent Document 1:JP-A 2006-045311 (U.S. Pat. No. 7,482,108)Patent Document 2:JP-A 2006-178317Patent Document 3:WO 2013/141222Patent Document 4:JP-A 2011-039266Non-Patent Document 1:SPIE Vol. 6520 65203L-1 (2007)